1,6-Difunctionalized hexane derivatives, in particular 1,6-hexanediamine, 1,6-hexanediol and adipic acid, are valuable compounds which are produced on a large scale in the chemical industry. These compounds are of commercial interest in particular for the production of polymers like polyamides, for example polyamide 6.6, polyesters and polyurethanes.
1,6-Hexanediamine is produced on a large scale in hydrocyanation reactions of butadiene with hydrogen cyanide to obtain adipodinitrile followed by a hydrogenation reaction. This process of the prior art particularly suffers from the use of hydrogen cyanide which is an expensive and toxic compound.
Adipic acid is produced in the industry mainly via oxidation of cyclohexanol with nitric acid. This process of the prior art is disadvantageous because nitrogen oxides are formed during the process from the nitric acid which have to be destroyed or employed in other processes. Furthermore, cyclohexanol is an expensive compound. The hydroxycarboxylation of butadiene with carbon monoxide and water to obtain adipic acid is known in the prior art. However, this process was never employed on a larger scale in the industry because it suffers from low selectivities for adipic acid and problems concerning its isolation.
1,6-Hexanediol is largely produced via hydrogenation of adipic acid. However, adipic acid is mainly produced by the process mentioned above. Therefore, the production of 1,6-hexanediol is connected with the same disadvantages.
In order to overcome the disadvantages of the processes for the production of select 1,6-difunctionalized hexane derivatives, different approaches have been suggested in the prior art.
U.S. Pat. No. 3,947,503 discloses a multi-step process for the production of 1,6-hexanediol from butadiene. In the first step, butadiene is subjected to a reaction with carbon monoxide and hydrogen in the presence of a rhodium complex and an alkanol or alkanediol to obtain the mono-acetal of 3-pentenal. In the second step, the mono-acetal of 3-pentenal is reacted with carbon monoxide and hydrogen in the presence of a cobalt complex. In the third step, the resulting mixture is subjected to a hydrogenation reaction in the presence of a hydrogenation catalyst. This process is disadvantageous for several reasons. It requires many steps and the yield of 1,6-hexanediol based on the starting material butadiene is low. In this process, a high amount of undesirable by-products is formed. The regioselectivity for 1,6-hexanediol is not satisfactory. Further, at least two different catalysts are necessary for this process. This process is also limited to the production of 1,6-hexanediol.
U.S. Pat. No. 5,312,996 discloses a process for the production of 1,6-hexanedial by the reaction of butadiene with carbon monoxide and hydrogen under catalytic reaction of rhodium complexes. Also reactions in the presence of diols are described. The yield of 1,6-hexanedial based on the starting material butadiene is low. A high amount of undesirable by-products is formed, in particular unsaturated and saturated mono-acetals and branched diacetals. The regioselectivity for 1,6-hexanedial is not satisfactory. A process for the production of 1,6-hexanediamine is not described.
The processes of the prior art are connected with disadvantages. The 1,6-difunctionalized hexane derivatives are obtained in low regioselectivities and low yields in the processes of the prior art. In known hydroformylations of 1,3-diunsaturated compounds, in particular butadiene, the regioselectivity for the 1,6-isomer of the dialdehyde over the undesirable 1,2-, 1,3- and 1,4-isomers of the dialdehyde is generally not satisfactory. The processes of the prior art yield a number of by-products.
In the hydroformylation of butadiene, these are particularly mono-unsaturated pentenals, pentanal and the undesirable regioisomers 1,2-hexanedial, 1,3-hexanedial and 1,4-hexanedial. The processes of the prior art are limited to the production of only select 1,6-difunctionalized hexane derivatives, in particular 1,6-hexanediol. Further, many of the processes of the prior art are energy and time consuming multi-step reactions.
Accordingly, it is an object of the invention to provide a process for the production of 1,6-difunctionalized hexane derivatives from 1,3-diunsaturated hydrocarbons, in particular butadiene, with a high regioselectivity for the 1,6-difunctionalized hexane derivatives. The process should be versatile and provide an universal route to different 1,6-difunctionalized hexane derivatives. With the process it should be possible to provide the 1,6-difunctionalized hexane derivatives in high yield. The process should particularly allow for the production of 1,6-hexanediamine, 1,6-hexanediol and adipic acid from butadiene with a high regioselectivity. With the process it should particularly be possible to obtain 1,6-hexanediamine, 1,6-hexanediol and adipic acid in high yield. Very particularly, it should be possible to obtain 1,6-hexanediamine in the process in high yield. The process should be performed economically without the need for many reaction steps.
The object of the invention is solved by a process wherein a 1,3-diunsaturated hydrocarbon, preferably butadiene, is subjected to a hydroformylation with carbon monoxide and hydrogen in the presence of a transition metal catalyst and an at least dihydric alkanol which can form an acetal with an aldehyde group, wherein during the hydroformylation the temperature is increased for at least 10° C. to obtain the mono-acetal and/or the di-acetal of the 1,6-hexanedial derivative. The acetals of the 1,6-hexanedial derivative are separated and further reacted to obtain the desired 1,6-difunctionalized hexane derivatives.
Surprisingly, it was found that the acetals of the 1,6-hexanedial derivatives can be obtained with a high selectivity for the 1,6-regioisomers and a high yield when an at least dihydric alkanol, which can form an acetal with an aldehyde group, is present during the hydroformylation of the 1,3-diunsaturated hydrocarbon with carbon monoxide and hydrogen and during the hydroformylation the temperature is increased for at least 10° C. The regioselectivity and the yield can be even further improved when during the hydroformylation the pressure of the gas mixture of carbon monoxide and hydrogen in decreased. The acetals of the 1,6-hexanedial derivatives can be separated, for example by simple distillation, and beneficially be employed as a starting material in further reactions, preferably an amination with an ammonia source, a hydrogenation or an oxidation, to obtain the desired 1,6-difunctionalized hexane derivatives, in particular 1,6-hexanediamine, 1,6-hexanediol and adipic acid.